The present invention relates in general to a refrigeration system and, in particular, to a refrigeration system with a hot gas defrost circuit having a reversing valve for periodic defrosting.
Various techniques for defrosting refrigeration systems are known. For example, a common method for defrosting a refrigeration system is to stop the refrigeration cycle and activate heaters placed near the evaporator coils. These heaters defrost and deice the evaporator coil. This method, however, is time consuming and often causes undesirable heating of the refrigerated area. Another method for defrosting refrigeration systems is to reverse the refrigeration cycle. When the refrigeration cycle is reversed, hot refrigerant vapor from the compressor is directed into the evaporator outlet, through the evaporator, into the condenser inlet, through the condenser, and back into the compressor. A problem with this method is that often the temperature of refrigerant entering the compressor is so low that some liquid is introduced into the compressor. This liquid may damage or destroy the compressor. In addition, the temperature of the refrigerant entering the evaporator is often too low for rapid or complete defrosting of the evaporator. Thus, the defrost cycle may be very time consuming or the evaporator may not be completely defrosted.
A conventional refrigeration defrost system is shown in U.S. Pat. No. 4,102,151 issued to Kramer, et al. The Kramer patent discloses a hot gas defrost system in which superheated refrigerant vapor from the compressor is routed through a tank filled with water. The superheated refrigerant vapor heats the water in the tank to a high temperature. The hot refrigerant then traverses the evaporator to defrost the evaporator coil. The refrigerant exiting the evaporator is then routed through the tank containing the hot water to reheat the refrigerant and ensure that all the refrigerant is in vapor form. The vapor refrigerant then enters the compressor to complete the defrost cycle. This defrost system requires a complex system of pipes, valves and a large water tank.
A conventional refrigeration defrost system is also shown in U.S. Pat. No. 5,056,327 issued to Lammert. The Lammert patent discloses a hot gas defrost system in which, during the defrost cycle, a series of valves and pipes are used to direct the refrigerant through the compressor, evaporator, condenser and back to the compressor, thereby utilizing the condenser as a reevaporator during the defrost cycle. The Lammert patent also discloses a superheater in a defrost passage which receives refrigerant from the condenser outlet during the defrost cycle and delivers it to the compressor inlet. Additionally, the Lammert patent discloses a passage which connect the compressor outlet and the evaporator inlet, that is, in a heat exchange relationship with the superheater in the defrost passage. The superheater allows heat from the hot vapor refrigerant discharged from the compressor to be used to heat the refrigerant delivered to the compressor inlet. This refrigeration defrost system undesirably requires numerous valves, pipes and a superheater to appropriately route the refrigerant during the defrost cycle.
Another conventional refrigeration system is disclosed in U.S. Pat. No. 5,050,400 also issued to Lammert. This Lammert patent discloses a refrigeration system including a series of valves and interconnecting fluid passages which allow refrigerant to flow sequentially from the compressor to the evaporator and, via a defrost passage, to the condenser and back to the compressor during the defrost cycle. This system includes a combined superheater/receiver located in the defrost passage for use during the defrost cycle. The combined superheater/receiver includes an inlet for receiving refrigerant from the condenser during the refrigeration cycle, a first outlet for delivering liquid refrigerant to the evaporator during the refrigeration cycle, and a second outlet for delivering refrigerant vapor to the compressor during the defrost cycle. During the defrost cycle, the system also employs a closed fluid conduit which uses the hot vapor refrigerant discharged from the compressor to heat the refrigerant entering the compressor. This closed fluid conduit ensures that all the refrigerant entering the compressor is in vapor form. Undesirably, this refrigeration defrost system requires extensive hardware, including numerous pipes and valves, to accomplish the appropriate routing of the refrigerant during the defrost cycle. This refrigeration system also requires the use of a superheater/receiver which adds to the complexity and cost of the system.
The present invention is an improved refrigeration system with a simplified hot gas defrost circuit that eliminates the complexities of conventional defrost systems. In one aspect of the invention, the refrigeration system includes a compressor, a condenser, an evaporator, an expansion valve, a defrost valve, and a reversing valve. During the refrigeration cycle, the reversing valve directs the flow of refrigerant from the compressor to the condenser, and the reversing valve directs the flow of refrigerant from the evaporator to the compressor. During the defrost cycle, the reversing valve directs the flow of refrigerant from the compressor to the evaporator and then to the condenser, and the reversing valve directs the flow of refrigerant from the condenser to the compressor. Advantageously, the present invention provides an energy efficient and cost efficient hot gas defrost refrigeration system, particularly in temperate and cold climates. In addition, the present invention eliminates the complex system of pipes and valves required in conventional defrost systems.
In another aspect of the invention the refrigeration system includes a receiver disposed between the condenser and the evaporator. During the refrigeration cycle, the refrigerant exiting the condenser bypasses the defrost valve and enters the receiver. The refrigerant then flows out of the receiver, through the expansion valve and into the evaporator. During the defrost cycle, refrigerant flows from the condenser into the compressor and refrigerant flows from the evaporator and into the receiver. The refrigerant then flows out of the receiver, though the defrost valve and into the condenser to complete the defrost cycle.
In yet another aspect of the invention, the refrigeration system includes two reversing valves. During refrigeration, a first reversing valve directs refrigerant discharged from the compressor into the condenser and a second reversing valve directs the refrigerant from the condenser into a receiver. The second reversing valve also directs the refrigerant from the receiver into the evaporator. During the defrost cycle, the first reversing valve directs the refrigerant discharged from the compressor into the evaporator and the second reversing valve direct the refrigerant from the evaporator into the receiver. The second reversing valve also directs the refrigerant from the receiver into the condenser. Advantageously, the two reversing valves eliminate the need for a second passage connecting the evaporator and the condenser.
Further advantages and applications of the present invention will become apparent to those skilled in the art from the following detailed description of the preferred embodiments and the drawings referenced herein, the invention not being limited to any particular embodiment.